The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro Injection for Weight Loss in the UK
Mounjaro is a prescription-only weekly weight loss injection now available in the UK through NHS specialist services and private prescribing routes. This dual GIP and GLP-1 receptor agonist works by helping regulate appetite and supporting feeling fuller after smaller meals. Clinical trials showed participants lost an average of 15–21% of their body weight when using Mounjaro alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly, and eligibility depends on your BMI and health circumstances. Our free BMI calculator can help you check whether you might meet NHS or private prescribing criteria.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
NHS Eligibility and Prescribing Criteria for Mounjaro
Mounjaro is prescribed in the UK for adults who meet specific BMI and health criteria. According to NICE guidance and NHS protocols, you may be eligible if you have:
- A BMI of 30 kg/m² or above (obesity), OR
- A BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds—eligibility may start at BMI 27.5 or above due to higher cardiovascular risk at lower weights. NHS access is through tier 3 specialist weight management services, typically accessed via referral from your GP. Waiting lists for NHS specialist services vary significantly by region (ICB), and availability can be limited. This is why many UK adults also access Mounjaro through private prescribing following an online clinical assessment with a UK-licensed prescriber.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Mounjaro Doses and Expected Weight Loss Results
Mounjaro is administered as a once-weekly KwikPen injection, starting at 2.5 mg and escalating every 4 weeks up to a maximum of 15 mg. Based on the SURMOUNT-1 clinical trial, participants on 15 mg lost approximately 20.9% of their body weight over 72 weeks—though results on lower maintenance doses were also significant (5 mg ≈ 15%, 10 mg ≈ 19.5%). These results were achieved alongside dietary changes and increased physical activity. Our free GLP-1 weight loss calculator can help you project potential outcomes at different doses, though individual response varies. Common side effects include nausea, diarrhoea, and constipation, typically most noticeable in the first few weeks of treatment.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for NHS prescribing through tier 3 specialist weight management services. However, NHS availability varies significantly by region, and waiting lists can be lengthy. Some ICBs have more limited access. Your GP can refer you to the specialist service in your area, or you can access Mounjaro privately through a GPhC-registered pharmacy following an online clinical assessment.
What is the difference between Mounjaro and Wegovy?
Both are prescription weight loss injections available in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly greater weight loss on average, though individual results vary. Both require a prescription and clinical assessment before being dispensed.
How long does it take to see weight loss results with Mounjaro?
Most people notice initial appetite reduction within 1–2 weeks, but meaningful weight loss typically takes 4–8 weeks to become apparent. Clinical trials measured results over 72 weeks, showing that sustained weight loss develops gradually alongside diet and exercise. Your GP or prescriber can monitor progress and adjust your dose if needed.
What happens if I stop taking Mounjaro?
If you stop Mounjaro, appetite regulation typically returns to baseline over 2–4 weeks, and weight regain can occur if dietary and lifestyle changes are not maintained. This is why Mounjaro is most effective as part of a long-term weight management plan rather than a short-term solution. Your prescriber will discuss this with you.
Is Mounjaro the same as the diabetes injection Ozempic?
No. Mounjaro (tirzepatide) and Ozempic (semaglutide) are different medications. Ozempic is approved for type 2 diabetes, while Mounjaro is specifically licensed for weight management. Mounjaro uses a dual mechanism (GIP + GLP-1), whereas Ozempic is GLP-1 only. Always use the medication specifically prescribed for you.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.